1. Field of the Invention
The present invention relates to improvements of a driving apparatus and a light-amount regulating apparatus which are suitably usable in a shutter device and the like provided in an image pick-up apparatus such as a digital camera. The present invention also relates to an improvement of a lens driving apparatus suitably usable in a lens driving mechanism provided in the image pick-up apparatus.
2. Related Background Art
A conventional shutter device of a lens shutter camera as illustrated in FIG. 17 has been proposed. In FIG. 17, reference numeral 101 designates a magnet member of a permanent magnet. Reference numeral 102 designates a driving lever. Reference numeral 102a designates a driving pin formed on the driving lever 102. The driving lever 102 is fixed to the magnet 101, and rotated together with the magnet 101. Reference numeral 103 designates a coil. Reference numerals 104 and 105 designate stators made of soft magnetic material, and magnetically excited by the coil 103, respectively. The stators 104 and 105 are connected to each other by portions 104a and 105a, and integrally arranged in a common magnetic circuit. Upon supplying current to the coil 103, the stators 104 and 105 are magnetically excited, and the magnet 101 is rotationally driven in a range of a predetermined angle.
Reference numerals 106 and 107 designate shutter blades, respectively. Reference numeral 108 designates a plate. Hole portions 106a and 107a of the shutter blades 106 and 107 are rotatably mounted on pins 108b and 108c of the plate 108, respectively. The driving pin 102a is slidably fitted into elongate holes 106b and 107b. Accordingly, when the driving lever 102 rotates with the magnet 101, the shutter blades 106 and 107 are rotationally driven about the holes 106a and 107a, respectively. An aperture portion 108a of the plate 108 is hence opened or closed. For purposes of preventing an increase in the cost, there has also been proposed a structure in which the magnet is comprised of a plastic magnet, and the driving pin is formed integrally with the magnet.
Reference numeral 109 designates a front plate for movably holding the shutter blades 106 and 107 between this front plate and the plate 108. Reference numeral 110 designates a rear plate for holding the stators 104 and 105, and rotatably holding the magnet 101.
Digital cameras for opto-electrically converting a field image and recording it as information of a still picture image in a recording medium by using a CCD and the like as a pick-up device have been more and more widely used. An example of the operation of exposure in those digital cameras will be discussed in the following.
The main power source is initially switched on prior to photographing to put the pick-up device in its operating condition, and the shutter blade is hence held at its open position capable of exposing the pick-up device. Accordingly, storing, discharging and transferring of electric charges are repeated by the pick-up device, and observation of the object field is made possible through the image monitor.
Thereafter, upon pushing the release button, stop value and exposure time are determined corresponding to the output of the pick-up device at that time. Accordingly, when the diameter of the exposure aperture needs to be narrowed, the stop blade is driven to be set at a predetermined stop value. Instruction of start of storing electric charges is then sent to the pick-up device from which stored electric charges are discharged. At the same time the circuit for controlling the exposure time begins to operate upon reception of that start instruction as a trigger signal.
After the lapse of a predetermined exposure time, the shutter blade is driven to its closed position for intercepting the exposure of the pick-up device. Upon intercepting the exposure of the pick-up device, the stored electric charges begin to be transferred. The picture image information is thus recorded in the recording medium through an image writing apparatus. Exposure of the pick-up device is blocked during the transfer of electric charges to prevent variation of electric charges due to undesired light during this transfer time.
Other than the above-discussed shutter apparatus, there also exist an apparatus with a mechanism for advancing or retracting an ND filter, and an apparatus with a mechanism for advancing or retracting a stop restricting member having a small stop diameter.
In the above shutter apparatus, the thickness can be decreased, but the coil and the stators are liable to occupy a wide area on the plate. In view of such disadvantage, a light-amount regulating apparatus as illustrated in FIG. 18 has been proposed.
In FIG. 18, reference numeral 201 designates a cylindrical rotor 201 whose portions 201a and 201b are magnetized to N and S magnetic poles, respectively. Reference numeral 201c designates an arm formed integrally with the rotor 201. A driving pin 201d extends from the arm 201c in the rotational axial direction of the rotor 201. Reference numeral 202 designates a coil disposed along the axial direction of the rotor 201. Reference numeral 203 designates a stator which is formed of soft magnetic material, and magnetically excited by the coil 202. The stator 203 has an outer magnetic pole portion 203a which faces the outer surface of the rotor 201, and an inner cylinder which is inserted into the rotor 201.
Reference numeral 204 designates an auxiliary stator which is fixed to the inner cylinder of the stator 203, and faces the inner surface of the rotor 201. Upon supplying electric power to the coil 202, the outer magnetic pole portion 203a and the auxiliary stator 204 are magnetically excited, and the rotor 201 is rotated up to a predetermined position. Reference numerals 207 and 208 designate shutter blades, and reference numeral 205 designates a plate. The shutter blades 207 and 208 are respectively rotatable about hole portions 207a and 208a into which pins 205b and 205c of the plate 205 are inserted, respectively. The driving pin 201d slidably engages with elongate holes 207b and 208b. Reference numeral 206 designates a torsion spring which gives elastic force to the rotor 201 such that the driving pin 201d can be pushed against ends of the elongate 207b and 208b. When electric power is supplied to the coil 202 to rotate the driving pin 201d together with the rotor 201 against the elastic force of the torsion spring 206, the shutter blades 207 and 208 are rotated about the hole portions 207a and 208a, respectively. The aperture portion 205a of the plate 205 is hence opened or closed.
A compact light-amount controlling apparatus can be achieved by such a light-amount regulating apparatus.
The light-amount regulating apparatus of FIG. 18 is more suitable for a small-sized structure than that of FIG. 17. In the light-amount regulating apparatus of FIG. 18, however, the shutter blades 207 and 208 can be simply held at either of their open positions or closed positions by changing the current supply condition of the coil only between ON state and OFF state. In other words, those light-amount regulating blades can be driven only between two states, i.e., a state in which the aperture portion is covered with them, and a state in which they are retracted from the aperture portion. Therefore, it is desired to provide an apparatus in which an intermediate open state between the above two states, for example, can also be established.
According to one aspect of the present invention, there is provided a driving apparatus which includes a rotor rotatable about its rotational axis and having a cyclindrical magnet portion whose outer circumferential surfaces are divided along a circumferential direction into plural differently magnetized portions; at least an outer magnetic pole portion formed extending in a direction parallel to the rotational axis of the rotor, and facing the outer circumferential surface of the magnet portion; an inner magnetic pole portion, and facing an inner circumferential surface of the magnet portion; and a coil for magnetically exciting the outer and inner magnetic pole portions, which is arranged along a direction of the rotational axis of the rotor.
In this driving apparatus, the rotor can be selectively held at one of three stop position, and a condition of xe2x88x920.3X+0.72 less than Y is satisfied where Y is a ratio of a central angle of each outer magnetic pole portion relative to a central angle of each magnetized pole in the magnet portion, and X is a ratio of a circumferential length of each magnetized pole in the magnet portion relative to a thickness of the magnet portion in its radial direction.
According to another aspect of the present invention, there is provided a driving apparatus which includes a rotor rotatable about its rotational axis and having a cylindrical magnet portion whose outer circumferential surfaces are divided along a circumferential direction into plural differently magnetized portions; an output member operative in response to rotation of the rotor; at least an outer magnetic pole portion formed extending in a direction parallel to the rotational axis of the rotor, and facing the outer circumferential surface of the magnet portion; an inner magnetic pole portion formed opposingly to the outer magnetic pole portion, and facing an inner circumferential surface of the magnet portion; a coil for magnetically exciting the outer and inner magnetic pole portions, which is arranged along a direction of the rotational axis of the rotor; a plate having an aperture portion; and a light-amount regulating member for changing the amount of light passing through the aperture portion upon being driven by the output member to advance toward or retract from the aperture portion of the plate.
In this driving apparatus, the light-amount regulating member can be selectively held at one of three stop positions, and a condition of xe2x88x920.3X+0.72  less than Y is satisfied where Y is a ratio of a central angle of each outer magnetic pole portion relative to a central angle of each magnetized pole in the magnet portion, and X is a ratio of a circumferential length of each magnetized pole in the magnet portion relative to a thickness of the magnet portion in its radial direction.
According to still another aspect of the present invention, there is provided a driving apparatus which includes a rotor rotatable about its rotational axis and having a cylindrical magnet portion whose outer circumferential surfaces are divided along a circumferential direction into plural differently magnetized portions; an output member operative in response to rotation of the rotor; at least an outer magnetic pole portion formed extending in a direction parallel to the rotational axis of the rotor, and facing the outer circumferential surface of the magnet portion; an inner magnetic pole portion formed opposingly to the outer magnetic pole portion, and facing an inner circumferential surface of the magnet portion; a coil for magnetically exciting the outer and inner magnetic pole portions, which is arranged along a direction of the rotational axis of the rotor; a plate having an aperture portion; and a lens for changing a focal length of a light beam passing through the aperture portion upon being driven by the output member to advance toward or retract from the aperture portion of the plate.
In this driving apparatus, the lens can be selectively held at one of three stop positions, and a condition of xe2x88x920.3X+0.72 less than Y is satisfied where Y is a ratio of a central angle of each outer magnetic pole portion relative to a central angle of each magnetized pole in the magnet portion, and X is a ratio of a circumferential length of each magnetized pole in the magnet portion relative to a thickness of the magnet portion in its radial direction.
According to those structures, there can be provided a simple driving apparatus in which the rotor can be held at its rotational position at which a boundary portion between magnetic poles of the magnet portion faces the outer magnetic pole portion, due to cogging torque acting between the magnet portion of the rotor and the stator, when no current is supplied to the coil; the rotor can be selectively rotated in one of different directions by changing the direction of current supplied to the coil; and three stop positions exist.
Other objects and advantages besides those discussed above shall be apparent to those skilled in the art from the description of a preferred embodiment of the invention which follows. In the description, reference is made to accompanying drawings, which form a part hereof, and which illustrate an example of the invention. Such example, however, is not exhaustive of the various embodiments of the invention, and therefore reference is made to the claims which follow the description for determining the scope of the invention.